Introduction to Ruby

# Computing Binomial Coefficients using Recursion
# nCr = (n-1)C(r) + (n-1)C(r-1)

def nCr(n,r)
  return 1 if n == r
  return n if r == 1
  return 1 if n == 0
nCr(n-1,r) + nCr(n-1,r-1)
end

n = gets().to_i
r = gets().to_i
puts nCr(n,r)

=begin
Sample Output:
~/work/ruby_tutorials$ ruby ncr.rb
10
3
120
~/work/ruby_tutorials$ ruby ncr.rb
10
4
210
=end

Check out some of our other Ruby Tutorials :

Introduction to Ruby

Introduction to Ruby and some playing around with the Interactive Ruby Shell (irb) Introduction to Ruby - Conditional statements and Modifiers: If-then, Unless, Case Introduction to Ruby Comments - Single and Multi-Line comments Introduction to Ruby Loops - Using While, Until, For, Break, Next , Redo, Retry
Introduction to Ruby - Arrays - Sorting, Filtering (Select), Transforming, Multi-Dimensional Arrays Introduction to Ruby - Strings Introduction to Ruby - Making a Script Executable Introduction to Ruby - Regular Expressions, Match, Scan
Introduction to Ruby - Computing Factorials Recursively : An Example of Recursion Introduction to Ruby - Binomial Coefficients (nCr) : An Example of Recursion Introduction to Ruby - Computing a Power Set : An Example of Recursion Introduction to Ruby - Towers of Hanoi : An Example of Recursion
Introduction to Ruby - Strings: Substitution, Encoding, Built-In Methods

Basic Data Structures With Ruby

Basic Data Structures in Ruby - Insertion Sort Basic Data Structures in Ruby - Selection Sort Basic Data Structures in Ruby - Merge Sort Basic Data Structures in Ruby - Quick Sort Functional Programming with Ruby
Basic Data Structures in Ruby - Stack Basic Data Structures in Ruby - The Queue Basic Data Structures in Ruby - Linked List - ( A Simple, Singly Linked List) Basic Data Structures in Ruby - Binary Search Tree